When you write in first person does it matter if your supporting cast are a bit like 2D cardboard cutouts? They would be the way the narrator thinks about them — Shaz the slag, Dad the fat lazy bastard, Dave the useless boyfriend, etc.

Yes it absolutely does. They are part of the world around your character, and that world has to be real.

They have be AT LEAST as real to the reader as they are to the "I" person. Sometimes a bit more depth then is required to keep the reader engaged and believing in your story.

Different characters need different levels of depth. The cashier at the store you visit once in your life does not have the debt of your characters current love interest. But they all have to appear to be real, IMO.

I kind of like the idea of the main character thinking of and treating at least some of the ancillary characters as "flat" (cardboard if you like) and then when they actually do something unexpected or unwanted, the main character gets upset.

"All I ever wanted was for her to split them when I had the urge, but then she gets all flighty and uppity, reads books, asks questions. WTF! I got no time for that kind of crap."

I don't think the characters need to be like the narrator thinks of them. The narrator has an interpretation, but it is just an interpretation.

True, but you do have preconceptions about people you know, especially if you have a slightly unusual worldview (which would be the only point of using first person). It's when they stray away from the narrator's expectations that this would come into play.

So in frahse's example above, with the wife reading a book it would make sense for the narration (from the man's perspective) say "Dang ho's pretending to read a book so she don't got to make my dinner." The reader couldl make their own mind up, but if it's told by the man it would be the way he sees things/people.

But I wouldn't be asking if I didn't think there was a problem with it myself...

I don't think the characters need to be like the narrator thinks of them. The narrator has an interpretation, but it is just an interpretation.

They have to be like the narrator thinks of them... or rather the narrator has to present them like he seem them. Unless you have multiple narrators, that means the views on all the characters will be skewed to what ever the narrator thinks. The reader will have read between the lines to find out if the narrator is right (you can not trust a first person narrator), but it still has to be presented from the point of view the book is written in.

True, but you do have preconceptions about people you know, especially if you have a slightly unusual worldview (which would be the only point of using first person). It's when they stray away from the narrator's expectations that this would come into play.

So in frahse's example above, with the wife reading a book it would make sense for the narration (from the man's perspective) say "Dang ho's pretending to read a book so she don't got to make my dinner." The reader couldl make their own mind up, but if it's told by the man it would be the way he sees things/people.

But I wouldn't be asking if I didn't think there was a problem with it myself...

"Hey man, it's a helluva lot worst than that. She reads these women's magazines. All a sudden, she's got questions about where OUR moneys going! About the future! Holy Hell, I don't need no bitching. I work every day. I got stresses!"

Actually wasn't wife, just live with long term girlfriend, but wife could work too. The point is, he wants her flat, to service a few simple purposes. To look good, bring in a paycheck, be good in bed, and otherwise keep quiet and not bother him. No need for her to be any more than that, to become a real person. That puts a load on him he doesn't want.
So basically the lady is trying to become 3 dimensional and that is a problem and this is not unusual by any count.

Every POV is a dual point of view - in this case, the narrator's and your own. You're seeing what the narrator sees, hearing what he hears, and reading what he thinks - but you're not turning your brain off in the process.

You're also seeing the narrator, by his words, thoughts and actions. Let's build on the current example. He's bitching about her reading a book. You see her reading a book. You hear him accusing her of trying to get out of making his dinner - which should be any ho's prime directive, natch. But in his words, his actions, his thoughts you also see that he's threatened by her reading. She's doing something that isn't all about him, something that can threaten his little world, his superiority. He's threatened by the implication that she might be smarter than him, that she's interested in things outside his boundaries, that her world is bigger than just him.

He never says any of it, but it's there. In turn, she becomes real, with motives and emotions of her own. If it's not there, then your narrator himself feels two-dimensional. Even the most myopic narrator should add life to the other characters through his POV, even if he himself believes they are no more than cardboard cutouts. Everything that makes him mad, makes him afraid, makes him happy with/about other people adds flavor to those other people.

I kind of like the idea of the main character thinking of and treating at least some of the ancillary characters as "flat" (cardboard if you like) and then when they actually do something unexpected or unwanted, the main character gets upset.

"All I ever wanted was for her to split them when I had the urge, but then she gets all flighty and uppity, reads books, asks questions. WTF! I got no time for that kind of crap."

Yes, this actually is a good device. I set up the blond bimbo in one of my books. Later, marine biologist.

When you write in first person does it matter if your supporting cast are a bit like 2D cardboard cutouts? They would be the way the narrator thinks about them — Shaz the slag, Dad the fat lazy bastard, Dave the useless boyfriend, etc.

How deep the character is, is dependate on the relationship to the narator and the narator's personality. So is the story teller is the plotting type and the charactor being thought of is their mortal enemy the deapth of the enemy would be great. However, if the narator was not a ploter but a silent doer the only thought might about the mortal enemy might be their bad they killed my mother - they stay in the shallow end of the pool.

One of the intresting thing I've try to do with the first person is show the characher by exposing their mis-consepctions. It's hard to work on how to expose the main character denial of reality when working in the first person.

Every POV is a dual point of view - in this case, the narrator's and your own. You're seeing what the narrator sees, hearing what he hears, and reading what he thinks - but you're not turning your brain off in the process.

There's actually a word for this in the industry. It's called an 'unreliable narrator' and it's a fairly common tactic in first-person narration.

A deft author can render secondary characters with enough detail to allow readers to form an opinion that conflicts with the views expressed by the viewpoint character, and the contrast between those two viewpoints can become an excellent source of literary tension.

The trick is to depict events and actions rather than just interpretations. It all comes back to the old adage of 'show, don't tell'.

There's actually a word for this in the industry. It's called an 'unreliable narrator' and it's a fairly common tactic in first-person narration.

A deft author can render secondary characters with enough detail to allow readers to form an opinion that conflicts with the views expressed by the viewpoint character, and the contrast between those two viewpoints can become an excellent source of literary tension.

The trick is to depict events and actions rather than just interpretations. It all comes back to the old adage of 'show, don't tell'.

There's actually a word for this in the industry. It's called an 'unreliable narrator' and it's a fairly common tactic in first-person narration.

A deft author can render secondary characters with enough detail to allow readers to form an opinion that conflicts with the views expressed by the viewpoint character, and the contrast between those two viewpoints can become an excellent source of literary tension.

The trick is to depict events and actions rather than just interpretations. It all comes back to the old adage of 'show, don't tell'.

Thanks for saying what I meant, which is much better then what I said!